1. Field of the Invention
The present invention relates to sailing craft and, more particularly, is directed towards hydrofoil sailboats having wingsails.
2. Description of the Prior Art
Over the years, there has been a continuous effort to increase the performance characteristics of sailing craft. Early sailboats were limited to sailing in a generally downwind direction. The capability to sail in a generally upwind direction increased with the slow evolution of hull, sail and rigging designs. With the advent of tacking sailboats, it became possible to travel at right angles to the wind or even in a slightly upwind direction. However, tacking sailboats required means for resisting the leeward drift and overturning moment which resulted from the sideward component of the force generated by the sail.
Several attempts have been made to improve sailboat design in the areas of speed potential and the ability to proceed in the windward direction. Hydrofoils have been used to raise the hull out of the water, greatly reducing hydrodynamic drag while still resisting leeward drift. Various hydrofoil configurations have been developed in order to increase speed and improve stability using either fully submerged or inclined surface piercing hydrofoils. However, such designs have had excessive low speed drag and have required high winds and high speeds to lift the hull free of the water. At higher speeds, most hydrofoil sailboats are plagued by air ventilation of the forward leeward hydrofoil which causes the hydrofoil to lose lift and suddenly submerge, resulting in a pitchpoling capsize.
Improvements in the capability of a sailboat to sail more directly into the wind came with the use of wingsails and rigid wings that employ more efficient airfoil shapes. Also, various non-vertical sails have been developed to reduce the overturning moment, such as the type shown in U.S. Pat. No. 3,295,487. Wingsails and rigid wings develop lift at lower angles of attack than a conventional bermudian sail can, and enable the sailboat to point up to 13.degree. closer to the wind. Symmetrical airfoil shapes are fixed and simple but develop about 10% less lift than a bermudian sail of the same size. Asymmetrical airfoil shapes can develop up to 50% more lift than a bermudian sail of the same size, but their asymmetry must be reversed when the sailboat tacks or reverses direction, and the mechanisms that have been developed to do this have been complex and heavy. Over the past several years, improvements have been made in the performance characteristics of hydrofoil sailboats. However, hydrofoil sailboats have met with varying degrees of success because of disadvantages relating to control, stability, and aero/hydrodynamic efficiency.